For over 100 years steel has been used to reinforce concrete structures. The steel can, for example, be provided in the form of cylindrical bars called "rebars" that are placed in a form prior to pouring concrete. Depending on the configuration of the structure being formed, such rebars can be bent into shape as necessary, one by one, and then tied together to form a steel skeleton or cage around which the concrete agglomerates.
Bending rebars individually, and then tying them in position on a steel skeleton, is time-consuming and requires a significant amount of labor and, thus, is expensive.
As an alternative to using individual rebars for forming steel reinforcing skeletons, welded wire fabric can be used. Welded wire fabric is a prefabricated reinforcement consisting of a series of longitudinal steel wires welded at selected intervals to transverse steel wires. Commonly, the size of the wires used can range from as small as about 0.1 inch in diameter to as large as about 0.6 inch or larger.
When first constructed, welded wire fabric is flat. Reinforcing skeletons of desired shape are formed by bending the transverse wires of the fabric to selected angles. Welded wire fabric as long as 20-21 feet (longitudinal wire length) having almost any width (transverse wire length) is commonly used.
Referring to FIG. 1, one example of a welded wire fabric 10 is shown in its flat configuration. The fabric 10 is made up of a plurality of transverse wires 12 welded to a plurality of longitudinal wires 14. Both wire size and spacing between adjacent wires are determined by construction design considerations. It is not uncommon to have spacing between adjacent longitudinal and adjacent transverse wires that is nonuniform. For example, although spacing between adjacent longitudinal wires 14 of the fabric 10 is uniform, spacing between the transverse wires 12 is not.
In the past, welded wire fabric bending machines have been provided to bend wire fabrics, such as the wire fabric 10, into a shaped skeleton of a desired configuration. For example, FIG. 2 shows an end view of the fabric 10 after it has been bent into an elongated U-shaped cage 16 for use in reinforcing a column. In this example, the transverse wires 12 are bent 90.degree. in the corners 18 of the U and are bent 135.degree. at their ends to form two opposed hooks or tails 20. When the U-shaped cage is in place, rebars 22 can be positioned along the length of the cage in both of the corners 18 and in both hooks 20 for additional reinforcement.
Referring to FIG. 3, a schematic, fragmentary elevation view of a typical prior art wire bending apparatus 24 useful for bending welded wire fabric into a desired shape, such as the U-shaped cage 16, is shown. The apparatus 24 has an elongated frame 26 extending along its length with an elongated track 28 mounted on top of the frame. A plurality of anvils 30 (only one of which is shown) are mounted on the track around which the transverse wires 12 of the mesh 10 are bent. Each anvil is on a carrier 32 having a rectangular cutout portion 34 that engages the track. The carriers can be moved along the length of the track and then fixed in desired positions, depending on the configuration of the wire to be bent.
A forming bar 36 extending along the length of the frame 26 is provided for bending the wires. The forming bar is connected to several arms 37 (only one of which is shown) that are pivotally mounted to the frame on the same side of the frame as the forming bar. Means, such as hydraulic rams 38, are provided to move the arms and forming bar to bend the wire fabric.
When using the apparatus 24 for bending a wire fabric, the fabric is placed on the apparatus with each transverse wire 12 extending under an associated anvil 30, i.e., between the bottom of the anvil and its carrier 32. For example, when bending a fabric, such as the fabric 10, into the U-shaped cage 16, 15 anvils are used since there are 15 transverse wires to be bent.
When forming the cage 16, the first bend provided is normally to form one of the hooks 20, both of which are usually required to be 3 to 4 inches long. In presently known benders, such as the bender 24, the perpendicular distance from the anvils 30 to the forming bar 36 is much farther than 4 inches and generally is about 9-10 inches or more. This large distance is provided so that the forming bar does not strike the anvils when the wires are being bent more than 90.degree., for example, when the wires are bent 135.degree. to form the hooks 20. Since the forming bar in presently known benders is farther from the anvil than the 3- to 4-inch length of the hook to be formed, two methods are now used for forming such hooks.
In the first such method, the hooks are formed by extending the ends 12a of the transverse wires 12 under the anvils so that the length of wire under the anvil, plus the length on the side of the anvil remote from the forming bar, is sufficient to form such a hook. The hydraulic rams are then actuated to force the forming bar against the wires 12 to make the bend. As is shown in phantom lines in FIG. 3, when such a bend is made the entire fabric 10, with the exception of the 3- to 4-inch hook portion, is forced over the top of the bender. As mentioned above, such fabric may be 20 feet long and can be 5 or more feet wide. Thus, several workers must be positioned on the side of the bender opposite from the forming bar to catch and support the heavy fabric as it is thrown over the top. Providing such extra workers is expensive. Additionally, the weight of the fabric when it is over the top of the bender tends to jam the hooks between the anvil and its associated carrier. This increases the time it takes to remove the hooks from under the anvils for repositioning the fabric for the next bend. Adding time to the bending process increases its cost.
The second hook 20 is formed by the same method used to form the first hook. Thus, the entire wire mesh must be lifted from the machine and turned around so that the ends of the transverse wires opposite the already-formed hooks are under the anvils and facing away from the forming bar. When the fabric has been repositioned, the above sequence is repeated, and again the entire wire fabric, with the exception of the 3- to 4-inch hook being formed, is forced over the top of the bender.
Removing the wire fabric from the machine and turning it around to form the second hook creates several problems. First, it is time-consuming and, thus, inefficient. Additionally when the spacing of the transverse wires is not uniform, it can be necessary to reposition the anvils along the length of the track to accept the fabric. Repositioning of the anvils increases the time of the operation and, thus, increases the cost.
As an alternate to forcing the entire fabric over the bender when forming the hooks, hooks having a length equal to the distance between the forming bar and anvil can be provided, i.e., about 9-10 inches or more. Depending on the size of the U-shaped cage being formed, such 10-inch hooks could, as shown in dashed lines in FIG. 2, close the U along its length. This is undesirable because the rebars 22 must then be placed into the U from above, rather than through the opening along the length of the U. Therefore, the ends of the hooks are cut off to reopen the U. Cutting the hooks is expensive, and, in any event, forming larger hooks than required results in an unnecessary waste of steel.
Although the prior art bender shown in FIG. 3 has only one forming bar assembly, one such bender is known to have been modified to include a second forming bar assembly essentially identical to the first. (The second assembly extends along the side of the machine opposite from the first assembly.) Such a dual forming bar bender (two-arm bender) has the advantage that both hooks can be formed without removing the fabric from the machine and turning the fabric around.
The distance from the anvils to the forming bars in the two-arm bender, however, remains greater than about 9-10 inches. Thus, the presently known two-arm bender has the same problems associated with forming the hooks as were described for the bender shown in FIG. 3. That is, extra workers must be provided to catch the wire fabric as it is forced over the top of the machine.
It is, therefore, desirable to provide to the art an efficient and easy-to-operate fabric bending apparatus on which short (3- to 4-inch) hooks can be bent without forcing the rest of the wire mesh fabric over the top.